Free piston engine development

Libertine’s Linear Power Systems technology is at the heart of Free Piston Research at one of Asia’s most prestigious international universities, the Universiti Teknologi PETRONAS (UTP) in Malaysia, supported by the PETRONAS oil and gas company.

Upstream oil and gas operations require reliable power generation since production often takes place in remote areas far from the electricity grid. Although there is often plentiful ‘raw’ gas available directly from the wellhead, current power generator solutions can struggle to deal with the variability of this unprocessed fuel and as a result there is a risk of costly power outages. UTP is investigating the role of free piston engines as a solution to this challenge. The variable compression ratio provided by this type of engine is ideally suited to generating power from variable quality fuels.

For over a decade, UTP has been undertaking advanced research and development on a suite of in-house linear generator and free piston research engine prototypes. Through this work, UTP have identified piston motion control as the key challenge that must be addressed before this research can be commercialised.

Libertine’s technology leverages a combination of piston geometry, electrical machine design and cylinder construction. All three are relatively long, each being several times the diameter of the cylinder bore. This novel architecture increases the electrical machine’s peak force relative to the moving mass of the translator, giving more effective and accurate control of the piston motion. Moving mass is kept to a minimum by integrating the electrical machine into the cylinder, rather than coupling a separate linear generator to a sealed combustion unit. Libertine’s elongated cylinder geometry also improves scavenging of burned gases to reduce tailpipe emissions and improves efficiency since at top-dead-center the combustion chamber has a lower surface-to-volume ratio, reducing heat losses.

Performance

Fuel type

Natural gas, hydrogen

Research engine format

Unbalanced single cylinder with bounce chamber

Bore

75 mm

Maximum stroke

400 mm

Compression ratio

Variable, 10:1 – 24:1

Operating frequency

12 Hz

Nominal power output

10 kWe

Specific force

>0.5 kN/kg

“UTP has an established programme of free piston engine research and development. We are building Libertine’s Linear Power Systems technology into our research engine programme to improve piston motion control and allow us to accelerate our research into high efficiency, fuel-flexible combustion systems.”